U.S.Defense Secretary Leon Panetta shakes hands with China's Vice President Xi Jinping before meeting September 19 in Beijing, China. Panetta is on a three-nation tour of Japan, China and New Zealand. (Larry Downing / Getty Images)

TAIPEI — Photos of a new Chinese stealth fighter, dubbed the J-21 and/or J-31, appeared on Chinese-language military blogs this week in time for U.S. Defense Secretary Leon Panetta’s trip to China.

It is unclear if the appearance of the photos was timed with Panetta’s trip, but the first photos of the Chengdu-built J-20 Black Eagle appeared the same week as former Defense Secretary Robert Gates’ visit to China in January 2011.

The new photographs show a twin-engine stealthy fighter with the number 31001 painted on its nose.

The number suggests it is the J-31 Falcon, said Richard Fisher, an Asia military affairs analyst at the Washington-based International Assessment and Strategy Center, but various Chinese-language blogs are debating the designation; with some suggesting it is the J-21 Snowy Owl built by Shenyang Aircraft Corp. (SAC).

In June, several videos appeared on the Internet showing a fighter fuselage, wrapped in a tarp, being transported along a highway from SAC to the Chinese Flight Test Establishment, an air force test center at Xian-Yanliang Airbase, Shaanxi Province. Whether the fuselage was the J-21 is still a matter of debate.

China’s military is not famous for its transparency, and cautious, educated guesswork is often the only indicator of what China’s military plans to field.

Photos of the new stealth fighter indicate it is smaller than the J-20 and lacks the forward canards, said Roger Cliff, a China air force analyst at the Project 2049 Institute.

Cliff suspects the J-31 might actually be the J-21.

Reportedly, the J-20 and J-21 were in competition for China’s stealth fighter competition, but the J-20 was rumored to have won. This might not be the case, Cliff said.

“The J-20 and J-21 could represent a high-low mix like the U.S. F-22 and F-35, the twist being that people have noted that the relatively large J-20 might be better for performing strike missions, like a modern version of the F-111, while the smaller-but-still-twin-engined J-21 might be better for air-to-air combat,” he said. “There’s precedent for that as well, with the larger [SAC] J-11B being a multirole aircraft while the initial versions of the smaller [Chengdu] J-10 were strictly air-to-air.”

An alternative possibility, Cliff said, is that the new fighter is intended for purely export, “which would explain why they have been at such apparent pains recently to make sure that people know about it.”

However, Cliff is skeptical about this alternative due to the lack of clarity on what a future non-F-35 fifth-generation fighter market is.

Analysts might have to wait until the Zhuhai Air Show in mid-November to discover more about China’s stealth fighter program.